What term describes a known plaintext attack that uses a linear approximation to analyze the behavior of a block cipher?

The term that describes a known plaintext attack that utilizes a linear approximation to analyze the behavior of a block cipher is Linear Cryptanalysis. This technique involves the identification of linear relationships between the plaintexts, ciphertexts, and the key bits in a cipher, which helps in deducing information about the key.

Linear Cryptanalysis works by leveraging known plaintexts and calculating how likely certain linear combinations of the plaintext bits, key bits, and ciphertext bits will yield specific results. This method allows attackers to gather statistical data and create approximations that improve the chances of determining the secret key. It represents an advanced form of cryptanalysis that can be particularly effective against certain block ciphers, especially if the attacker can gather enough data.

The other options do not accurately describe this specific method of cryptanalysis. For example, Block Cryptanalysis is not a commonly used term in the context of known plaintext attacks with linear approximations. Statistical Analysis, while related to interpreting data in cryptography, is a more general approach that encompasses various techniques, not limited to linear relationships. A Man-in-the-middle Attack refers to a different type of attack where an adversary intercepts communications between two parties, which is unrelated to the analysis of block ciphers.